Process of heat treating powdered metal parts



Oct. 9, 1956 H, L. CROWLEY ETAL PROCESS OF HEAT TREATING POWDEREID METAL. PARTS Original Filed Ju ne 6, 1950 4 Sheets-Sheet 1 PRESSED 47 2.6,000 E61] LEGEND.

Oct. 9, 1956 v H. L. CROWLEY EI'AL 2,766,117

PROCESS OF HEAT TREATING POWDERED METAL PARTS Original Filed June 6, 1950 4 Sheets-Sheet 3 PKESSED #7 25000 5.]

0 1 2 s 4 5 6 7 a 9 1o H cl PRESENT INVENTORS lfenry lrawleq By llarwn Emlsi fimfian WAQM RENEE Q m &

MN m N\ a E N h W k w H. L. CROWLEY EIAL 2,766,117

PR VESS OF HEAT TREATING POWDERED METAL PARTS 4 Sheets-Sheet 4 Oct. 9, 1956 Original Filed June 6, 1950 IN VEN TORS Henry Z1. frdur'lly BY 11411011 [17165; (rrrlhzm United States Patent PROCESS OF HEAT TREATING POWDERED IVHETAL PARTS Henry L. Crowley, South Orange, N. J., and Marion Ernest Graham, Parma, Ohio, assignors to Republic Steel Corporation, Cleveland, Ohio, a corporation of New Jersey Substituted for abandoned applications Serial No. 166,312, June 6, 1950, and Serial No. 300,908, July This application April 3, 1956, Serial No.

17 Claims. (Cl. 75-224) The present invention relates to a process of heat treating powdered metal parts and more particularly to heat treating and/or sintering such parts formed by pressing powdered metal into a desired shape in order that the parts as heat treated or sintered shall have desired physical characteristics.

As such the present application is a continuation-inpart of our prior and copending application Ser. No. 300,908, filed July 25, 1952, and now abandoned, and entitled, Process of Heat Treating Powdered Metal Parts and Parts Formed Thereby; said application Ser. No. 300,908 in turn being a continuation-in-part of our earlier application Ser. No. 166,312, filed June 6, 1950, and now abandoned. It is intended that the present application shall be a substitute for each of the earlier applications here identified.

In the past it has been customary in the making of parts by so-called powder metallurgy practices to select the powder of one or more metals, mix if powders of more than one metal are used, compact this powder in a suitable mold under relatively high pressure, then sinter the pressed parts in a non-oxidizing atmosphere at a suitable temperature, which is chosen in respect to the composition of the parts, in order that the metal powder shall be bound together into the desired article. Parts so formed are usually not as strong as a part made from cast metal, but they have the advantage that little or no machining need be done following the formation of the desired part in this way. As a result, the parts may be given adequate mechanical strength for some particular purposes, not requiring the strength of cast metal parts, and at the same time be made much quicker and cheaper. Such prior art processes have been applied using single metals and using combinations of metals, usually by mixing the powders of two or more metals in desired proportions. The atmospheres in which the heat treating or sintering has been done are uniformly non-oxidizing in character, but within that limitation, have been of many different types. All this prior art practice is now quite well known and is described in numerous text books on the subject.

The present invention improves this prior art practice in a substantial manner in that parts may be formed and heat treated in accordance with the present invention, so as to have greatly enhanced physical properties, for example, tensile strength, elongation and hardness, when heat treated at the same temperatures that would have been used in accordance with prior art practices. Alternatively, at least as good physical properties may be im parted to a given part as in the prior art, while using substantially lower temperatures for the heat treating than was thought possible in accordance with prior art practices. Intermediate results may be obtained in accordance with the present invention, including somewhat enhanced physical properties as aforesaid, While using somewhat lower temperatures than were considered standard in accordance with the prior art teachings.

The present invention further improves on prior art practices in that by using the same conditions of temperature, the same results, or even better results, may be ob tained in a shorter time period. Alternatively, the temperatures may be somewhat lower than have been standard in the prior art for various metal combinations respectively, and the same rate of production may be attained by resorting to the processes of the present invention. In other words, articles may be formed with the same or enhanced properties in respect to corresponding prior art articles, but in a shorter time and sometimes also at a lower temperature.

Summarizing the present invention, the processes in accordance therewith all involve heat treating in an atmosphere including gaseous hydrogen chloride. The improvements in the physical properties of the parts made according to the present process are more or less proportionate to the concentration of hydrogen chloride in the atmosphere about the parts during the heat treatment, in most instances up to about 10% to 15% hydrogen chloride concentration in this atmosphere by volume. For the purposes of the present invention, the-minimum amount of hydrogen chloride in the atmosphere may be taken to be about 0.1% gaseous hydrogen chloride by volume. The enhanced physical characteristics of the final product reach their peaks for most of the metals and combination thereof as hereinafter set forth at about 10% to about 15% by volume gaseous hydrogen chloride in the atmosphere, so that it is pointless to use any higher percentages; and in fact from some points of view, as hereinafter set forth, the use of higher concentrations of hydrogen chloride may be undesirable. It is found further that when the gaseous atmosphere surrounding the part during the heat treating contains some reducing gas, as hydrogen, correspondingly better results are attained as compared to the use of a completely neutral gas, as nitrogen. The metals which are susceptibe to forming into parts in accordance with the present invention are broadly, the relatively difficultly chloridizable metals, namely, one or more metals selected from the group consisting of (a) the metals: iron, copper, nickel and cobalt and mixtures and alloys consisting essentially of at least two of said metals, (b) mixtures and alloys corresponding generally to bronze and consisting essentially of up to about 10% tin and the balance copper, (0) mixtures and alloys corresponding generally in composition to ferrous base alloys and consisting essentially of:

up to about 4% carbon,

up to about 20% tungsten,

up to about 1.75% manganese, up to about 28% chromium,

up to about 8 /2% molybdenum,

and the balance in any such composition iron, whereon iron is present in a predominant amount.

Some relatively easily chloridizable materials do not lend themselves to treatment in any manner similar to. the present invention. Examples of such materials are zinc, aluminum, magnesium, titanium and alloys containing a substantial proportion of one or more of these metals. Such materials are to be considered as positively excluded from the scope of the appended claims.

Considering now details of the present invention and the principles governing it, there will be discussed first the metal or metals which may be used in accordance with this invention. Broadly, as aforesaid, the metals usable are practically restricted to those metals which are V relativelyidiliicult to chloridize.

7 above, trouble is encountered.

' fot the metal particles substantial amounts of and the prior art srof s ppl o priate metals and alloys is giyen above. This list includes all the metals now known to be usable, singly or in com-' bination, in metal parts which may be processed in accord. ance with the present invention.

7 In the event that some one of the relatively easily chloridizable metals, such as zinc, aluminum or rn'agnesiurn', be present any sub 'stantial amount, either alone, as an ingredient of'fa mixture, or as one metal forming an {alloy with some'other metal or metals which may be in the "acceptable list given 7 For example, brass, an alloyconsisting of copper and'z'incfls not to be considered as included in the purview'of the 'pfocess'e's set-forth in the present claims; in contrast with this, bronze, consisting essentially of copper and up to 10% tin may be formed and heat treated in accordance with the present invention and within the scope 'of "the appendedclaims This will appear more particularly in examples hereinafter given.

The present invention is applicable when one or more metals are used, whether the metals, if two or more, be

introduced 'as separate powders of the-individual metals.

or as. alloy powders, i. e. Wher'ein each particle of the powder is an alloy. Whenseparate powders of individual metals are originally used in making the parts, there is considerable evidence that there is increased inter-diffusion when operating 'in'accordance with the process of the present invention as compared with prior art processes. v

The theory, which is now believed to be basically cor 'rect, but is not particularly relied 'uponin support of the patentability of the appended claims, "is that when sub stantial amounts "of diza ble metals are attacked by the hydrogen chloride to such an extent that the dizab-le metals and/or is porous due to the volatilization of such chlorides, leaving spaces for merlyoc'cupied'by'the chloridized metals. ln'eithe'r event, thereresultsa p'roduct, different in composition from the metal powder which was subjected to the pressing operation and introduced into the heat treating step, which product has, in fact,

hydrogen chloride are "present in the atmosphere during heat treating, relatively easily chlor'i:

final product has present therein the chlorides of the easily chlorigen chloride is derivcd from a source separate'and indeness, in respect to articles madein the same way throughout, with the exception that the atmosphere in which they are heat treated contained no hydrogen chloride.

These differences will be apparent from particular .ex- 7 amples hereinafter given and from the accompanying drawings. I V The advantages to be gained by the presence of hydrogen chloride in the gases surrounding the articles in the heat treatment is more or less proportionate to the.con-' centration of hydrogen ClllOl'lJB, in that greater advantages are gained in the caseof most of 'the 'm'eta ls and alloy'sf listed above by using higher percentages .of hydrogen of certain physical characteristics against hydrogen chlo-. ride concentration levels off. Based upon plof-ts'of this kind, such as are shown in the accompanying drawings, is the principle of this invention that any amount of hydrogen chloride is advantageous, so long as the hydropendent of the presence of any intermixed chlorides in the parts being treated, for example, when the hydrogen chloride is supplied as 'such in gaseous form to the gases,

which are supplied from some external source to and/or a are. passed through the 'chloridi zing zone. The same results cannot be obtained,howeyenby reliance upon the less desirable physical characteristics than would 'be-present. if prior art practices were employedusing a nonoxidizing atmosphere without hydrogen chloride present I therein. a

The next majorfactor to bejconsidered in the present case is the. atmosphere which is 'to be used during the heat treating. This fatmosphere must be essentially 'nonoxidizing in character. It ma'ygbe neutral or reducing', but cannot be to any substantial extent oxidizing. Many such atmospheres (absent hydrogen chloride) have been tried in theprior art, so that no particular'details need be' given-here of the large number of different possible nonoxidizing atmospheres'which are usable. It is found,

.- howeven'in actual tests, 'as'more particu-larly'evident from examples given hereinafter, that nitrogen, a neutral gas, in operative as the non-oxidizing atmosphere. it has been found, however, that when the atmosphere surrounding the parts during'the heat'treat-ment used is reducing in character, such as a gas containing'or consisting of hydrogen (other than the hydrogen chloride present therein), better results are obtained than with a strictly neutral gas.

Thus, the preferred atmosphere, in accordance with. the present invention,

proportion of hydrogen.

is one-in which there is a'subst'antial The theories now avail'able tending to explain this will be stated hereinafter;

The jessential distinction between the presentinve'ntion V is in t'hefus'e of some gaseous hydrogen chloride. as a part of the atmosphere surroundin the metallic parts during the heat treatment'there'of. "It is V found that when this process is carried 'o'n,fthe "parts as fi'nally'made and as a result of the heatftr'eatme'rit, have enhanced ph sical characteristics of tensile trehgthand usually also of elongation, and t'o sonie extent also, 'h'a'rd generation ofhydrogen chloride in situ adjacent to the articles by supplying some chloride inter-mixed with the metal powder making up the articles being treated and by supplying some gaseous hydrogen in the atrnospheiesur rounding the articles for reaction with such intermixed chloride to produce hydrogen chloride, or even by sup- 7 plying as an admixture in the articles a decomposable chloride, such as ammonium chloride, which may pose under the temperature conditions present to 'give hydrogen chloride. It is believed that this is due to the fact that under such conditionsyoids are left'in the metallic body being sintered which results in'a decrease in the strength, which such articles would otherwise have. As

hereinafter more particularlyfsctout, when the amount oi" V intermixed chloride is very smaihthe undesired restilts' 'of its presence may be overcome bythe enhanced and j desired results due to the presence of sufficient, separately introduced hydrogen chloride in the gases, sothat final product will haveprope'rties "superior to prior art articles. a

Inorde'r that the present invention maybe easily understandable by those skilled in the art, an arbitrary value of 0.1% hyd-rogen'chloride is hereby stated as the minimum hydrogen chloride concentration in the gas by volume which will be'considered'to'be Within the limits of this invention.

. concentrationofhydrogen chloridein accordance withthe towards chloridizing some present invention is from about 0.5% to about 10% by volume. For maximum advantages from the point or view of physical characteristics 'of the final product, in accordance with the prese'nt invention, 5% to about 15 has been found to be prefier'redfor most metals'a'nd combination thereof to which the invention is applicable. Beyond 15% there seems to be'no pur'pose in increasing the hydrogen chloride concentration as the costs of the operation are increased to some extentjand the physical properties of the final product, not-substanin additionto this, asthe concentrationof hydrogcn'chloride 'in the gases is raised, the tendency.

tially better.

' of the metal present is some what'increa'sed.

This point is relatedto the theories now believed to be correct for the use of an atmosphere containing some Taliingiron; for example,

reducing gas, as hydrogen.

there is aprogressively increasing tendency, asthe-hydro. 7

gen chloride concentrationis increased, fora reaction to occur between the iron and hydrogen chloride tofofrrn fer'toli s ehloride. If "any ferrous chloride 'be formed,

decorr- I those of V,

definite and i Avpr'eferred range, however, of

the range of about.

even instantaneously, any hydrogen present in the gases will tend to reduce it to reform iron and to liberate hydrogen chloride in gaseous form. Thus, from an overall point of view, the presence of hydrogen in the atmosphere tends to prevent the formation and possibly the subsequent volatilization of ferrous chloride. Corresponding reactions can occur between other metals present and hydrogen chloride. For this reason, it is usually preferred to keep as low a hydrogen chloride concentration as possible, consistent with obtaining desired results, while at the same time having some hydrogen present in the gases. Another factor to be considered is the tendency for gases containing hydrogen chloride to corrode the apparatus in which the process is carried on. Here again, in order to minimize such corrosion, it is usually desirable to use as low a concentration of hydrogen chloride as can be used, while still obtaining the advantages of the present invention in producing articles having enhanced physical properties.

In contrast with the above, it is the present theory that when hydrogen chloride is used in accordance with the present invention in an atmosphere consisting, apart from hydrogen chloride, of a neutral gas such as nitrogen, there are opposing effects. The presence of hydrogen chloride will give enhanced physical characteristics in the final product in accordance with the present invention. On the other hand, the presence of hydrogen chloride, in the absence of a strongly reducing gas, such as hydrogen, will result in some chloridizing of the metal. This in turn will result in relatively less desirable physical properties. The net result, as will appear hereinafter from an actual example, is that physical properties somewhat enhanced in respect to those resulting from prior art practices are obtained when using hydrogen chloride and a neutral gas; but these properties are not as desirable respectively as are the properties of a corresponding article, heat treated in about the same concentration of hydrogen chloride in a gas also containing hydrogen. Preferably, however, the hydrogen concentration in a gaseous mixture including a neutral gas should be substantially equal to the proportion of hydrogen chloride therein.

Several theories have been formulated tending to explain the novel and highly beneficial results obtained from the practice of the present invention. One of these theories is that the hydrogen chloride present acts in a manner similar to a pickling bath, in that it serves to clean the surfaces of the metallic particles by removing any oxide film therefrom. This leaves the particles with clean surfaces, which are enabled more efficiently to sinter together, so as to form a superior article under a given set of conditions. The removal 'of the oxides thus results in enhanced physical characteristics for the final articles.

Another theory, which perhaps partakes of the above theory to some extent, is that the hydrogen chloride present in the gases reacts with any metallic oxides present to convert them to the respective chlorides. These chlorides, in a process in which the gases contain some hydrogen, may be reduced; and the reduced metal so formed may then act as a cement or binder to bind the particles of the original metallic material together. In such an event, the hydrogen chloride acts in effect as a catalyst, as it is regenerated by the reduction reaction with hydrogen.

Another theory which is in some respects related to the theory just explained is that hydrogen chloride may react with some of the finer of the metallic particles, converting them into the respective chlorides and generating hydrogen. Then some hydrogen, the same o'r'some other hydrogen or both, present in the gases, may then react with the chlorides formed to regenerate the metals, but this time to deposit metal respectively so as to cement together or to increase the size of those particles and the bonds therebetween in a manner similar to that in which crystals grow in a solution. In such an event also the hydrogen chloride acts in effect as a catalyst, as it is regen- .erated and not consumed to a substantial extent.

While the theories expressed herein are now believed to be correct, the p'atentability of the appended claims is not predicated upon the correctness of these theories, or any of them, but rather upon the novel combination of process steps specifically recited herein. It is not known exactly why theseimproved results occur. It is known, however, that they do in fact occur and that they are reproducible when the teachings of this application are followed.

It appears that the hydrogen chloride must be present in gaseous form in the atmosphere surrounding the articles, and that this gaseous hydrogen chloride must be obtained at least in a large part from some one or more sources other than decomposition of a chloride introduced in admixture with the metallic material, or resulting from a reaction between such intermixed chloride and any hydrogen in the gaseous atmosphere. by the fact that while gaseous hydrogen chloride was effective in securing enhanced physical properties in an iron body or article, no correspondingly desirable results were attained when using an atmosphere as in the prior art including hydrogen and when chloride was supplied in the form of solid ferrous chloride intermixed with the iron powder as a part of the article to be heat treated. This was so even though the atmosphere used surrounding the ferrous chloride-containing-article consisted solely of hydrogen. This result was surprising in view of the fact that it is known that in 'an atmosphere of hydrogen, ferrous chloride is largely reduced to metallic iron at the temperature and in the time at which these articles were held for heat treatment. Under the circumstances of the test, wherein the powdered iron article contained a relatively large amount of solid FeClz, the article produced had a lower physical strength as compared with an article formed of pure iron powder and heat treated in accordance with the prior art at the same temperature. From this it was concluded that in order to attain the desired results of the present process, it is not feasible to supply chloride as solid ferrous chloride intermixed in the article itself, so that hydrogen chloride must be otherwise supplied to or be present in the gases surrounding the article during the heat treatment.

As hereinafter set forth by examples which follow, a very small amount of intermixed chloride, for instance an amount in the order of magnitude of 0.1% to 0.25% by weight, will have such a small undesired effect upon the tensile strength of the final article that when such an article is sintered in an atmosphere containing hydrogen chloride from an external source, in accordance with the present invention, quite desirable results are obtained. When the percentage of the intermixed chloride is as high as about 0.25, the undesired results thereof begin to be substantially felt. Progressively greater amounts of intermixed chloride give progressively worse results in terms of the tensile strength of the final article. There is a point at which the desired results of the use of separately introduced hydrogen chloride in the gases will not serve to overcome the undesired results of intermixed chlorides in the original article. When greater amounts of intermixed chloride than this amount, to balance the desired results of hydrogen chloride, are present, the net effect of both on the tensile strength of the finished article is undesired in respect to following prior art practices. The preferred situation, therefore, is one in which the metallic material formed into the articles to be sintered is free, or substantially free, of any intermixed chloride, as under these circumstances there is no, or substantially no, undesired eifect therefrom, so that the desired effect of the presence of hydrogen chloride in the gases is not diminished by this opposing effect.

The next major factor to be considered in the present process is the temperature at which the heat treating takes place. In accordance with the prior art wherein the gaseous atmosphere did not contain hydrogen chloride, such temperatures were in fact standard, or substantially This was proven tent also hardness.

so, for any given metal or combination of metals. For example, with powdered iron, the temperature used was about 2000" F. This standard temperature, chosen in accordance with the. prior art, may be defined as that at which at least one metal present is brought to the point ofincipienf fusion. At the same time, these standard temperatureswere always less than the melting point of theihighest melting metal present. As such, therefore,

the temperatures varied substantially depending upon the composition of the 'metal or metals contained in the part being'heat treated; For the purpose of the present discu ssion, these prior art sintering temperatures in an atmosphere in which hydrogen chloride was absent may be termed'sta11dard temperatures. Such standard temperat'ures'may be found in many text books and articles treating this subject matter. r a r In accordance with-the present invention the process may be practiced at the standard temperature as aforesaid for the'materialin question and thereby greatly enhanced physical characteristics obtained in the final article, particularly tensilestrength, and elongation, and to some ex- This practice may be termed one phase of embodiment ofthe'p'rese nt invention. 7 1

Another phase or embodiment of the presentinvention is to conduct the sintering operation at substantially reduced temperatures in respect to standard temperatures as aforesaid respectively. At such reduced temperatures, which are substantially less'than the standard temperatures for any given metal composition, at least as great or .as desirable physical properties may'be attained in the final'pr'oduct'as would result from the practice of prior art processes with respect to the same type article. For example, taking the case of an iron article, the standard temperature of the prior art is about 2000 F. when using an atmosphere containing no hydrogen chloride. In accordance with the present invention, a final article formed from iron powder can be prepared using a sintering temperature of about 1600 F. and having at least as desirable combinations of these several'variables as herein taught may be employed within the purview of invention. V

In the accompanying drawings there are illustrated graphically some of the desirable results of the present invention, so that these results may be visualized more the present easily than could bedone from mere tabulated results. i

in the drawings:

Figure l is a plot showing the relation between the tensile strength and sintering temperature in iron articles previously pressed at 25,000 'p. s. i. and with different concentrations of hydrogen chloridepresent in the atmosphere during the sinterin g;

Fig. 2 is a plot similar to Fig. 1, but with the articles pressed at 50,000 p. s. i.;

physical properties of strength and elongation. .Thu s, in

accord-ance'with this embodiment of the process of the invention, substantially less heat is required, with a corresponding saving in the cost of the heat and in wear and j tear on. the equipment usedincident to'the use of higher 7 temperatures.

Intermediate practices may alsobe used in accordance with the present invention using temperatures between the'st a'ndard temperature and the lowest temperature possible as aforesaid, which may be expressed as somewhat lower than the standard temperatures, and attaining results somewhat more desirable than those attainable in I accordance with prior art practices.

It'is also contemplated in accordance with the present invention, that a temperature may be used, when heat treating a metallic article including two or more metals, which temperature will be below the melting point of the highest melting metal present, but not necessarily below the melting po'intof one or more'lower melting metals Another phase or embodiment of the present invention is that by employing an atmosphere including hydrogen chloride, in accordance with this invention, desired results at a given'temperaturel may be obtained in a somewhat less time thanwas required when-operating ,in ac cordance with prior art pra'ctices, wherein no hydrogen chloride was present in the atmosphere. Thus, for a given temperature, and as the time period for the sintering of a given article may be shortened by following the practice of ,the present invention, a given piece of equipment will have increased productivity in any time period, such as a dayor a week. This desired shortening of the sinteringtime may be effective to render the processmoreidesirable from an economic point of view and Fig. 3 is a plot showing the relationship between tensile strength and the concentration of hydrogen chloride pres ent in the gaseous atmosphere during sintering, curves being shown for different temperatures, the material used being iron powder pressed at 25,000 p. s. i.; and

Fig. 4 is a plot similar to Fig. 3, but with the articles pressed'at 5 0,000 p. s. i. rather than 25,000 p. sci.

In each of the plots shown in the accompanying drawings, a comparison is given with the prior art, which is that condition represented by 0% hydrogen chloride. It

will be noted from the several plots that substantially enhanced results as to tensile strength are obtained when progressively greater concentrations of hydrogen chloride are present in the gases up to about 10%; and thatthese results are diiferent to a substantial and surprising extent from those obtainable using prior art practices. While the data forming the bases for the curves shown in the I drawings was obtained using powdered iron test pieces;

similar results are obtainable using other metals or combinations as setforth herein; a

The data illustrated in Figs. 1 through 4 is set forth in tabular form in Tables 1 and '2 below. The Rockwell hardness values. referred to in Table 2 were obtained using a standard Rockwelltest apparatus employing a /8" steel ball and a .60 kilogram major load. All readings given are H scale readings.

. TABLE I Iron powder pressed at 25,000 p. s. 1. before heat treatment Tempera- Tensile Elonga- Percent H01 in Atmosphere ture, F. Strength, tion,

. p. s. i. Percent 1,200 270 0. 1,200 370 0. 1, 200 310 0. 1,200 680 1. 1, 200 900 0. 1, 200 1, 330 0. 1, 400 4, 360 1. 1,600 5,760 1. l, 600 5, 1. 1,600 5,680 2. 1, 600 6, 080 2. 1, 600' 6,640 3. l, 000 8, 330 4. 1, 800 6, 580 1. 1,800 5, 060 1. 1,800 ,510 2. l, 800 7 420 3. 1,800 8, 590 3. 1, 800 9, 260 4. 2,000 7, 260 2. 2, 000 7, 560 2. 2, 000 7, 760 2. 2,000 7, 510 r 2. 2,000 9,150 3. 2, 000 11,540 5.

TABLE 2 Iron powder pressed at 50,000 p. s. 1. before heat treatment ercen 1n emperaens e onga on, P t HCl T T 11 El ti Atmosphere ture, F. Strength in Percent R. C

in p. s. i

1, 200 830 0. 3 1, 200 1, 240 0.8 1, 200 1, 480 1.1 a 1, 200 1, 250 0. 9 1, 200 1, 930 1. 1, 200 2, 960 1.1 1, 400 8, 830 2. 8 1, 600 10, 080 1. 6 1, 600 11, 190 3.1 l, 600 10, 800 3. 1 1, 600 10, 700 3. 6 1, 600 12, 400 4. 7 1, 600 14, 110 6. 2 1, 600 14, 560 5. 4 1, 800 11, 230 3.1 1, s00 11, 970 2. a 1, 800 12, 620 3. 4 1, 800 12, 970 3. 4 1, 800 15, 530 3. 7 1, 800 15, 640 5. 8 2, 000 13, 300 3. 4 2, 000 1a, 640 3. 9 2, 000 13, 350 4. 2 2, 000 15, 23 5. 2 2, 000 16, 550 5. 2 2, 000 680 7. 4 2, 000 17, 650 7.

From Tables 1 land 2 above, it will be noted that the results obtained in terms of tensile strength and elongation for the tests made using lower concentrations of hydrogen chloride are somewhat spotty and irregular. Nevertheless, it is believed that desirable results may and often will be obtained, at least as to certain of the physical characteristics, even with relatively low concentrations of hydrogen chloride. On the other hand, it will be obvious from the tabulated data given above, that the preferred concentrations are the relatively higher ones, approaching 10%, at which positively improved results are always obtained in respect to prior art practices wherein no hydrogen chloride was used.

Additional tests were made on this same type of iron, as set forth in Tables 1 and 2 above, and at both '1600 F. and 2000 F., with the parts pressed at 50,000 p. s. i. as in Table 2 above, the percentage hydrogen chloride in the sintering gases being increased in these several tests to include the values of 50%, 75% and 100% hydrogen chloride with the balance (it any), hydrogen. The values of tensile strength were approximately constant within the limits of experimental error, and increased but slightly up to 100% hydrogen chloride, the value of the tensile strength at 100% hydrogen chloride, at 2000 F., averaging 17,920 p. s. i. From the above, it is concluded that concentrations of hydrogen chloride in excess of about 15% do not give any substantial increase in the tensile strength of the finished articles.

The application of the process of the invent-ion to powdered metals other than iron may be illustrated by the following examples:

Example 1.--Powdered metal parts consisting of 92.5% iron powder and 7.5% copper powder by weight were produced by mixing copper and iron powders in these proportions and pressing the mixed powders to shape at 50,000 p. s. i. Some of these parts were then sintered in a pure hydrogen atmosphere at 1800" F. for one hour. Others of these parts produced under the same conditions were sintered for the same time and at the same temperature in an atmosphere consisting of 90% hydrogen and 10% hydrogen chloride gas by volume. The tensile strength of the part sintered in pure hydrogen was 16,000 p. s. i., these parts having an elongation of 1.5%. The corresponding parts that were sintered in the atmosphere containing 10% hydrogen chloride had a tensile strength of 22,230 p. s. i. and an elongation of 1.5%. This illustrates that sintering in atmospheres containing hydrogen 10 chloride has a beneficial eficct on thetensile strength of copper-iron mixed powders. 7

Example 2.--Metal parts were prepared by mixing 97% of iron powder and 3% of nickel powder by weight and pressing the mixed powders at 50,000 p. s. i. Some of these parts were sintered for 1 hour in an atmosphere of pure hydrogen at 18-00" F., while others, having the same composition, were sintered under the same conditions of time and temperature in an atmosphere consisting of hydrogen and 10% hydrogen chloride gas by volume. The parts sintered in pure hydrogen had a tensile strength of 11,280 p. s. i. and an elongation of 3.1%; while other parts of the same composition sintered in the atmosphere containing hydrogen chloride had a tensile strength of 13,720 .p. s. i. and an elongation of 4.2%

Parallel tests were also run on powdered metal parts which were prepared in the same way, but which consisted of 94% iron and 6% nickel by weight. Of these samples, the ones sintered in a pure hydrogen atmosphere had a tensile strength of 11,980 p. s. i. and an elongation of 3.2%; while those that were sintered in an atmosphere consisting of 90% hydrogen and 10% hydrogen chloride by volume had a tensile strength of 14,450 p. s. i. and an elongation of 3.4%. Here again, the advantageous results of sintering in an atmosphere containing hydrogen chloride gas are demonstrated by an increase in tensile strength of the order of 20%, while there is also an increase in percentage elongation.

Example 3. Powdered metal parts (simulating bronze), consisting of 90% copper powder and 10% tin powder were prepared .by mixing these two powders and pressing the mixed powders to a desired shape at 50,000 p. is. i. Some of these parts were sintered for one hour in an atmosphere of pure hydrogen at a temperature of 1475 F; while others were si-ntered under the same conditions in an atmosphere consisting of 90% hydrogen and 10% hydrogen chloride gas by volume. Those parts sintered in pure hydrogen had a tensile strength of 14,040 p. s. i. and an elongation of 0%; While those sintered in the atmosphere including hydrogen chloride gas had a tensile strength of 29,500 p. s. i. and an elongation of 8. 6%. In this mixture, particularly, the [advantages of sintering in hydrogen chloride-containing atmospheres are strikingly illustrated.

Example 4.As an example of the application of the invention to gases of a non-reducing, neutral character, the results of sintering powdered iron parts in a nitrogen atmosphere are set forth below. Samples were prepared from the same type of powdered iron employed in the tests, the results of which are shown in Figures 1 through 4 and are set out in Tables .1 and 2 above, by pressing the iron powder to a desired shape at 50,000 p. s. i. Some of the test pieces so prepared were sintered for one hour at 1800 F. in an atmosphere of pure nitrogen, while others were sintered under the same conditions in an atmosphere consisting of 90% nitrogen and 10% hydrogen chloride gas by volume. Those test pieces sintered in the atmosphere of pure nitrogen had an average tensile strength of 11,130 p. s. i. and an average elongation of 0.9%; while those sintered in the atmosphere containing hydrogen chloride had an average tensile strength of 14,320 p. s. i. and an average elongation of 2.1%. Thus, it will be seen that when using a neutral atmosphere, such as nitrogen, the addition of hydrogen chloride enhances the physical properties of heat treated powdered metal parts. However, it will be noted by comparison with the data set [forth in Table 2, that this increase of tensile strength is not as great as when the heat treatment is carried out in an atmosphere containing hydrogen.

During the tests on the heat treatment of iron articles in an atmosphere of nitrogen and hydrogen chloride,lthe presence of FeClz was observed in the exit gases. It is believed that during such a process the beneficial effects of the hydrogen chloride were partially counteracted by the formation and subsequent volatilization of FeClz,

, as hydrogen.

V 1 1 which weakened the product physically to some extent. However, this undesired chloridiza-tiondid not take place to such an extent-as toiprev e n't the hydrogen chloride from "enhancing'the tensile strength ofthe parts in respect to that of parts sintered in an atmosphere containing no hydrogen chlonidej This example thus further illustrates the beneficial efiec-ts of the presence of a reducing gas,

A further seriesof tests was conducted upon some nitrogen and varying amounts of hydrogen and hydrogen chloride. It was found that the best values of tensile strength were obtained when approximately equalsconeentna tions of hydrogen and hydrogen chloride were present along with nitrogen, and that the requirements for hydrogen chloride in the gases in order to obtain maximum tensile strength indicated that products having increased tensile r'strength would be obtained up. to about 10% hydrogen chloride. QThus, substantiallyfthe optimum con ditions are reachedwith a gas concentration (by volume) of 10% hydrogen chloride, 10%1hydrogeh and 80% nitrogen giving a tensile strength for iron parts comparable to the tests set, forth in Table 2 aboye (iron powder pressed at 50,000 p. s. i. and sintered at2000 F.),Yo f 17,260 pj-s. i. With 30% hydrogen, 30% hydrogen chloride and 40% nitrogen, tensile strength averages 1 8,950p. s. i.;

r whi'le with 30% hydrogen chloride, 60% hydrogenand 10% nitrogen, tensile strength averages 18,98011 s. i.

From the above, it will be seen that little increase in V tensile strength of the finished parts is attained by using more than about 10% hydrogen chloride. Furthermore,

these ,tests have shown that'when less than'about the equivalent amount of hydrogen in respect to hydrogen chloride is used, relatively lesser tensile strengths are obt ained as set forth above. It is believed that the opti mum conditions, therefore, are reached when substantially equal amounts of hydrogen and hydrogen chloride are terial containing a substantial amount of zinc. This expect-at-ion was proved accurate by the tests made in lac-' cordance with this example. Test samples were pre pared from the brass alloy powder'descnibed above, by Some of the samples so made. 7

pressing at,5-0,000 p. .s. i. were s-intered for one hour in an" atmosphere of pure hydrogen at l620'F., while others were sintere-d under 'the same conditions in an atmosphere consisting of 90% tion, which was found'when the process of the present application was applied to these parts, is believed to be attributableto the factth-atithe relatively reactive Zinccontaining powder combines with the hydrogen chloride gas to forrri zinc chloride, which volatilizes at the tempera tures employed, leaving the remaining structure'of the part substantially weakened. As such, therefore, the general teachings of thep-re'sent invent-ion are not applicable to zinc-containing powders or parts.

Example 6.--The presence of solid chloride in admix ture with .a powde-red'metal part exerts an undesirable influence upon the resulting tensile strength of the part. This; matter has been. investigatedv from various points of-lview, .the investigationinaooordance with the tests herein reported on using iron powder and Ian-hydrous ferrous chloride, as an example of a chloride, so that react-ion between ferrous chloride and hydrogen in the gaseous atmosphere would provide the same metal of which the part was made. Several samples were prepared by incorporating and intermixing various proportions of solid anhydrous F eClz with the powdered iron part being treated. The results of this series of tests (in which the parts were exposed to an atmosphere -oonsistingesseh tially of hydrogen and wherein hydrogen was a still; atmosphere, no attempt was made to circulate the hydrogen past the articles during the heat treatment, so as to permi t the building of a'hydrogen chloride concentration, if such were reasonably possible) are set ytqrth in Tables 3 and4hereina-fter given. ,7 s

'I ABLE 3 Iron powder pressed at 25,000 p. s. i." befor e"heqt treaty ment .l

Tempera- Tensile" Elongation Porcent'oolid FeClz in Mixture ture, F. Strength; in Percent.

0 1,800 6, 580 1 .1' 1, 800 5, 050 1. 5 1, 800 5, 370 V 1. 5 1, 800 t 5, 280 l 5 TABLE .4 g Iron powder pressed at 50,000 12. s. i. before heat treatmen! 7 Tempera- Tensile Elongation Percent Solid. F0012 in Mixture ture, F. Strength, in Percent V p. S. i.

1,800 13,940 2.2 1, 800 r 12, 670 l. 6 1, s00 13, 550 a. 7 1, 800 10, 490 V V 2, 4

possible except-ion of trace amounts, present as impurities;

7 It has also been found that the presence offerrous chlo-i ride in admixture with a powdered iron part has an eifect which is variable, depending upon the time and conditions of exposure of the part to the atmosphere '(basedon the Water vapor content thereof) between the admixing of the powder and pressing operation on the one hand, and the sintering operation on the other. This is believed to be due to the fact that anhydrous ferrous chloridetends to take up water from the atmosphere, probably forming some one or more of the hydrated ferrous'chlorides; and that this tendency is not wholly. prevented even though parts are kept in a desiccator during theinterval, be: tween pressing and sintering. As a'result, it hasibeen found that when a substantialrinterva-l, such as aday or two, intervenes between the pressing and the subsequent sintering of the parts, and even if the parts after pressing are'stored in a desiccator, such parts have irregular and relatively undesirable strength characteristics, as measured by the tensile strength of the final products.

When parts were formed as aforesaid, having but a very small amount of admixed ferrous chloride therein;

and when these parts were sintered within not over ten minutes from the time of pressing to the time of introduction into the 'sintering oven, and when the sintering tool; place in the presence of hydrogen chloride gas de rived from a source independent of the admixed ferrous chloride, the undesired effect of the admixed ferrous chloride, was offset by the desired effect of the practice Tensile Strength Percent H01 in the Sintering Gas in p. s. 1.

These results may be compared with a set of similar samples containing 0% FeClz and tested in the same way which are as follows:

Tensile Strength in p. S. 1.

Percent H01 in the sintering Gas From the above, it will be noted that the tensile strengths resulting from the tests using 5% and hydrogen chloride in the gases are better than when no hydrogen chloride is present. More desirable results are obtained, however, when from 5% to 10% hydrogen chloride is used. On the other hand, the tensile strengths of the parts having 4% FeClz are respectively lower than those of the parts containing no admixed FeClz.

It is believed, therefore, that the presence of admixed chloride introduces an undesired effect which may be partly or wholly offset by the desired change or efiect due to sintering the part in an atmosphere containing hydrogen chloride derived from a source separate and independent of the reaction between hydrogen present in the gases with admixed FeClz; and that this is true irrespective of the presence of hydrogen in the sintering gas. It is, of course, possible that the undesired etfects resulting from the presence of admixed ferrous chloride or other chloride will be so great as wholly to negative the desired result from the use of the hydrogen chloride containing atmosphere in-accordance with the present invention, so that the net effect may be a poorer product than if neither were used or present.

It is preferable, therefore to minimize and more preferable to reduce to zero the amount of admixed ferrous chloride in accordance with the present invention, so as to realize to a maximum extent the desired results of the present process.

Example 7.This example is to illustrate the application of the present process to articles made from nickel powder. Parts were prepared of nickel powder by pressing this powder at 30,000 p. s. i. (all that was required for a resonably dense green compact) and then sintering at 2000 F. Different samples were sintered with gases having different hydrogen chloride (HCl) concentrations as set forth hereinafter. A sample of nickel prepared as aforesaid and which was sintered in an atmosphere of pure hydrogen had a tensile strength of 7,930 p. s. i. and an elongation of 4%. Another sample sintered in an atmosphere including 1% (by volume) hydrogen chloride and the balance hydrogen had a tensile strength of 8,520 p. s. i. and an elongation of 4.0%; while a sample which was sintered in an atmosphere consisting essentially of 10% hydrogen chloride and the balance hydrogen had a tensile strength of 11,390 p. s. i. and an elongation of 4.7%.

From the above it will be noted that when the process of the present invention was used, there was a substantial (and in the case of 10% HCl, a very material) increase in tensile strength and a certain amount of increase in elongation.

Example 8.-Tests were made of the applicability of the present invention to parts made of 100% copper. In this instance copper powder was compacted at 20,000 p. s. i. and sintered at 1400 F., these values being found to be applicable in the case of copper. A group of samples was tested after being sintered indifferent gaseous compositions, i. e. compositions including dilferent concentrations of hydrogen chloride, with the balance hydrogen in each instance. The test results showed that when sintered in an atmosphere of pure hydrogen, the parts had an average tensile strength of about 12,000 p. s. i. and an average elongation of about 6.7%; when sintered in an atmosphere consisting essentially of 1% hydrogen chloride and the balance hydrogen, the parts had an average tensile strength of about 12,900 p. s. i. and the same average elongation, i. e. 6.7%; while when sintered in an atmosphere of about 10% hydrogen chloride and the balance hydrogen, the parts had a tensile strength of about 17,050 p. s. i. and an average elongation of about 9.4%. This is deemed to show that the use of the process of the present invention with parts made of copper powder positively increases the tensile strength of the parts by very substantial amounts and increases the elongation somewhat, but again by a substantial amount.

Example 9.--Parts were prepared using metallic cobalt powder 300-mesh size and made up using a pressing pressure of 60,000 p. s. i. and were later sintered at 2000 F. The tensile strengths of parts made using different amounts of hydrogen chloride mixed with hydrogen, were as follows:

Tensile Strength This indicates that the maximum strength as to articles of substantially pure cobalt is attained at a value between 1% and 5% (by volume) hydrogen chloride, the tensile strength falling off somewhat at 10%, but still being greater than that when no hydrogen chloride is used.

Example 10.Parts were prepared using about 5% cobalt powder as in Example 9 above, and about Swedish iron powder, the parts being pressed at 60,000 p. s. i. and later sintered in a gas consisting essentially of various percentages (by volume) hydrogen chloride and the balance hydrogen, 'at 2000 F. The results of these tests are shown in the following table:

Tensile Strength in p. s. 1.

Percent HCl in the sintering Gas Hon-c com ' drogen chloride and the balance hydrogen.

- "f chloride and the balance hydrogen, at 2000 F. The results are shown in the following table:

Percent H 01 in the Sintering Gas Similar tests were made using about tungsten with thebalance iron. In these tests, agroup of test bars was made of this composition and sintered in pure hydrogen.

The average tensile strength of these bars was 7,950 p. s. i. and the average elongation, 3.0%.

Another group of test bars of the same composition (about10% tungsten with the balance iron) was prepared and sintered in a gaseous mixture consisting essentially of about5% hy- These bars showed upon testing an average tensile strength of 14,400 p. s. i. and an elongation of. 4.5%. This shows a definite increase in tensile strength and in elongation respectively for the'bars which were sinteredin accordance with the present invention. V

" Another similar group of test bars was prepared and V 7 tested, the compositionv of which consisted essentially of about tungsten and the balance iron. A group of.

these test-bars was sintered in. pure hydrogen and then tested with the results: tensile strength (average) 6,600 p. s. i., elongation (average) 2.4%. A further group of test bars made up in the samewlay and of the same com- 7 position (about 20% tungsten and, the balance iron) was the resulting parts, using difierent' percentages (by vol- 'ume) of hydrogen chloride with the balance hydrogen as a sintering atmosphere, are shown in the following table: r

Tensile Strength Percent H01 the Sintering Gas e in p. S. i.

Example 13.Parts were prepared of 0.25% molybdenum powder admixed with the balance of pure Swedish iro'n powder, pressed at 50,000 p; s. i.,;a-nd thereafter sintered at '2000 F. The tensi le strengths ,for the resulting parts, using ditieren-t percentages .(by volume) of hydrogen chloride with the'ba-lance hydrogen as a sintering atmosphere,are shown in the following table;

Tensile Strength Percent I-IOl in the Sintering Gas in p. s. i.

Further tests weremade to illustrate the application of the present process to compositions having a substantially higher'molybdenum content. 1 11 the first group of these spasm 'denum and the balance iron.

tests, compositions were made up with about 4% molyb- A group of testbar's of this composition was sintered in pure hydrogen and then tested. These bars showed an average tensile strength of 18,100 p. s. i. and an average elongation of 3.9%. V ilar group of test bars of the identical composition and mode of preparation was sintered in a gaseous atmosphere consisting essentially of'about 5% hydrogen chloride and the balance hydrogen. These bars, when tested, showed an average tensile strength of 19,800 p. s. i. and an average elongation of 4.9%. In this instance it is noted that, while the avarage tensile strength is but little higher when following the practice of the present invention the elongation found was substantially greater. .7 a 7 A further group of tests bars'with a still higher molyb denum content was'p'repared. In this instance the com position was about 8 /2% molybdenum with the balance iron. A group of such test bars was prepared and sintered in pure hydrogen and then tested, withthe test results showing an average tensile strength of 19,030'pqs. i; and an average elongation of 5.8%. A'sirnilar group of test bars of the identical composition (about 8 /2 molybdenum and thebalance iron) was sintered in anati i mosphere consisting essentially of about" 5% hydrogen chloride and the balance hydrogen Thebars of this group, when tested, showedan average tensile strength of 26,300 p. s. i. and an average elongationof 5.7%.-

In this instance it is noted that the elongation is substantially the same whenusing the process of the present.

invention as .without it, but the tensile strength is very substantially enhanced. This example was prepared for V the purpose of illustrating a high limit of molybdenumcontent to which the present invention is believed applicable.

Example chromium powder admixed with the balance of pure Swedish iron powder, pressed at 50,000 p. s. i., and thereafter sintered at. 2000 F. The tensile strengths for. the resulting parts, 'using diiierent percentages (byvolume) of hydrogen chloride with the balance hydrogen asa sintering atmosphere, are shown in the following table:

Tensile Strength Percent H01 in theSinterlngGas in p. s. i.

From. the above, it will be noted that the maximum strength in iron-chrome parts is attained at a. value under; 10% hydrogen chloride in the atmosphere and closer to 5%, although the parts made and sintered in the 10% hydrogen chloride atmosphere were about twice as strong .as those sintered in an atmosphere of pure hydrogen.

, Further tests have been made to illustrate the application of the process to compositions having substan chromium and the balance iron (the chromium being tially'higher contents of chromium. in a first group of these tests the-starting composition was about 4% added in the form of ferro-chromium having a 67.7% chromium content). A group of tests bars of this composition was sintered'in pure hydrogen and then tested' with the test results showing a tensile strength (average) of 5,170 p. s. i. and an elongation of 2.4%. A' second group of test bars of the same composition was sintered in an atmosphere consisting essentially of 5% hydrogen chloride and the balance hydrogen and then tested. The test results in this instance showed an average tensile strength of 8,5001). s. i. and an average. elongation of 2.3%. Summarizing these results, it is. noted that the practice of the present process resulted in very'substantial enhancement of the tensile strength while the elongation' remained substantially constant.

A Sim:

14.--Parts were prepared of 1.05%'

A further set of test bars was made up using a maximum limit of chromium for the present invention, i. e. about 28% chromium, with the balance iron (the chromium being added as aforesaid as a 67.7% ferrochromium alloy). In this instance the average test results of a group of bars sintered in pure hydrogen was 2,260 p. s. i. as to tensile strength and 0.8% as to elongation; while a group of bars of the same composition, sintered in accordance with the present invention in an atmosphere consisting essentially of about hydrogen chloride and the balance hydrogen, showed test results of 2,570 p. s. i. as to tensile strength and 2.0% as to elongation. Here it will be noted that, while the presence of chromium in substantial amounts appears to reduce the tensile strength under all circumstances, the practice of the present invention results in some substantial enhancement of the tensile strength and a very substantial enhancement in the elongation as contrasted with prior art practices involving sintering in pure hydrogen.

Example 15.In view of the very desirable results in the increase of tensile strength for a number of binary alloys as herein given, it was thought that the present invention could be advantageously used on a material substantially equivalent in composition to a standard stainless steel. Such a composition was made up in powder form and was substantially 19% chromium, 1.6% manganese, 9% nickel and the balance iron. A series of test bars was made of this composition by pressing at 50,000 p. s. i. and then sintering in each instance at 2000 F. A first group of these test bars was sintered in pure hydrogen and showed an average tensile strength of 3,240 p. s. i. and an average elongation of 2.4%. A second group of test bars of this identical composition was made up in the same way and sintered as aforesaid in an atmosphere consisting essentially of 5% hydrogen chloride and the balance hydrogen. This group of bars, when tested, showed an average tensile strength of 5,600 p. s. i. and an average elongation of about 2.1%. Thus it is deemed that the process is applicable to multi-metal alloys such as stainless steels, wherein, however, the composition is within the limits herein set out for the several binary alloys, which have been made and tested as aforesaid. The fact that the elongation is slightly less for material produced by the present process is not 'considered prohibitive as it is well within tolerable limits.

Example 16.The parts in this group were made up of 98% Swedish iron powder and 2% graphite, pressed at 60,000 p. s. i. andthen sintered at various temperatures and under conditions as set forth in the following table:

Tempera- Tensile Atmosphere ture, F. Strength 1, 800 12, 500 1,900 15, 000 2,000 26,000 1, 800 23,000 90% Hz, 107 1, 900 28,000 90% H2, 10% E01 2,000 28, 500

These tests are deemed to indicate that iron-carbon alloys, simulating steel, follow the trend set forth in the application and show substantially increased tensile strengths when the process of the present invention is employed in connection with the sintering.

Further tests were made to illustrate the application of the process to even higher carbon contents in iron. To this end a group of samples was made up using Swedish sponge as a source of iron, this being a commercially available type of iron powder, and using carbon in each instance in the form of graphite. These tests employed a composition consisting essentially of about 4% carbon with the balance iron. All bars of this composition were found to be very brittle and to have a very low, and in effect insignificant, elongation. For this reason no data as to elongation are given. The bars were all made by pressingthe composition at 60,000 p. s. i. and sintering at 2000 F. for one hour. A group of three such bars, when sintered in pure hydrcgen, was found to have an average tensile strength of about 28,650 p. s. i. Another group of three such bars was prepared as aforesaid of the identical composition and mode of preparation and sintered in an atmosphere consisting essentially of 10% hydrogen chloride and the balance hydrogen. This group Was found to have an average tensile strength of 32,470 p. s. i. It is believed, however, that about 4% is the maximum carbon content which is reasonably tolerable in a ferrous base alloy as aforesaid. Such an alloy in all instances in this case is considered to be one having a'substantial preponderance of iron, i. e. substantially over 50% even in instances where quite large percentages of alloying constituents are present, such as stainless steel.

While the process of the present invention has been disclosed as applied to a limited number of the many possible combinations to which it is applicable, the principles herein set forth are applicable generally 'within the limits stated. It is intended that the appended claims shall be construted to cover all reasonable equivalents as will occur to those skilled in the art from the foregoing particular disclosure, and that the claims should be construed validly as broadly as the state of the prior art permits.

What is claimed is:

1. The process of making metallic parts starting with a metallic material consisting essentially of at least one of the relatively difficulty chloridizable metallic powders selected from the group which consists of (a) the metals: iron, copper, nickel and cobalt and mixtures and alloys consisting essentially of at least two of said metals, (b) mixtures and alloys corresponding generally to bronze and consisting essentially of up to about 10% tin and the balance copper, (0) mixtures and alloys corresponding generally in composition to ferrous base alloys and consisting essentially of:

up to about 4% carbon,

up to about 20% tungsten,

up to about 1.75% manganese, up to about 28% chromium,

up to about 8 /2% molybdenum,

and the balance in any such composition iron, wherein iron is present in a predominant amount; said process comprising the steps of compacting a predetermined amount of said material by mechanical pressure to form it into a green pressed blank having a shape and size predetermined'in accordance with'the shape and size of the part to be made, and thereafter heat treating said green pressed blank in a non-oxidizing atmosphere containing at least about 0.1% of gaseous hydrogen chloride by volume, and wherein said hydrogen chloride is introduced into said atmosphere from a source separate and independent of any chloride which may be present in admixture in said metallic material, by raising the temperature of said material of said blank to a point at which at least one metal present is brought to the point of incipient fusion in said atmosphere, and by supplying hydrogen chloride gas to said atmosphere from a source independent of the material making up the parts being treated.

2. The process in accordance with claim 1, wherein the volume concentration of gaseous hydrogen chloride in said atmosphere is about 0.5% to about 10%.

3. The process in accordance with claim 1, wherein the volume concentration of gaseous hydrogen chloride in said atmosphere is about 5% to about 15%.

4. The process in accordance with claim 1, wherein said non-oxidizing atmosphere also contains hydrogen.

5. The process in accordance with claim 1, wherein said non-oxidizing atmosphere consists essentially of a mixture of gaseous hydrogen chloride and hydrogen.

6. The process in accordance with claim 1, wherein said heat treatingis carried on at'substantially? the same" temperature at which some one metal presentin said metallic materialwill sinter in the same atmosphere with-- out hydrogen chloride present therein, so as t'o'produce a part having enhanced physical properties inrespect to the corresponding physicalproperties of such a part sintered in the same atmosphere but withouthydrogen chloride therein.

7; The process inaccordance with claim- 1, wherein said heat treatingis carried on at a temperature substantially below that temperature at which some one metal present in said metallic material'willsinter in the same atmosphere in the absence of hydrogen: chloride therein,-

- so as to producea part. having. substantially asi desirable physical' properties as the part would have if sintered in the; same atmospherein: the absence of. hydrogen chloride thereinat the" temperature at. which some: metal. present 7 will sinter in. the absence ofhydrogenchloride.

this'metallic material would sinter in such atmosphere in which hydrogen chloride was absent.

9..'1 he process in accordance with: claim 1,, wherein said metallic material used informing the metallic parts to be treatedis s'ubstantially'free of all intermixed chlorides, whereby all the hydrogen" chloride present in said non-oxidizing atmosphere is supplied thereto froma source external of the parts being sintered. 170i The process in accordance with claim 1, wherein said metallic material consists essentially of iron and copper and wherein said atmosphere, containsfrom about to about hydrogen chloride by volume, the temperature of the heat treatment being at'least that at which copper powder is brought to the point of incipient fusion.

11. The process in accordance with claim 1, wherein said metallic material consists essentially of up to about 4% carbon and the balance iron, and wherein said atmosphere contains from about 5% .toabout 15 gaseous hydrogen chloride by volume.

12. The process in accordance with claim 1, wherein said metallic-materialconsists essentially ofmetallic iron, and wherein said atmosphere contains from about 5%.

.to' about 1 5%" gaseous-hydrogen chloride by volume,

2e 13 Theprocess in. accordance with'claim 1, wherein said metallic material consists essentially of (iron and": nickel, and wherein said atmosphere contains from about;

5-%'to about 15 gaseous hydrogen-chloridebyavolumea' the temperature of the heat treatment being at least that; at which nickel powder is brought to the pointot incipient fusion. t

14.- The process in accordance'with claim 1, wherein said metallic material consists: essentially ofuptoabout? 10% tin and thebalance copper, and whereinssaid atv rncsphere contains from about 5% to about. 15 gaseous hydrogen chloride by volume, the temperature: of the heat treatment being atleast that at which brought to'thepointof incipient-fusion. I

1 5;- The process in accordance with claim 1, wherein; saidheat treatment was carried on-for a. time periodlsub:

stantially less than that in which a part of. the'samef composition: would be sintered in. the same atmosphere without hydrogen chloride present. therein,v so as t 12 30? vide for increased production. of sinter'edparts havinggat least as good physical properties as would be provided if. such parts were sintered for the conventional time in. the same atmosphere without hydrogen chloride present therein.

16. The process in accordance with claim 1, wherein said heat-treatment is carried on at subs'tantiallythe same temperature at'which a part having the same composition would be sintered in' the same atmosphere but without hydrogen chloride present therein, and fora time period substantially less than has been conventional for sintering sucha part in such an atmosphere but without hydrogen chloride, so as to" provide; for increased production" of sintered' parts each having at least as good physical prop erties as would be produced from the sameunsintered parts if sintered' in the same atmosphere at the same temperature butwithout hydrogen chloride-present.

' l7. Theprocessrin accordance with claim 1, wherein the heat treating step aforesaid is carried on in a'sintering Zone, wherein said non-oxidizingatmosphere is maintained in said sintering zone by substantially continuously passing through said zone a non-oxidizing gas'eousmedium including at least 0.1% (by volume) gaseous hydr'o gen chloride as aforesaid, and wherein said gaseous 11yrogerr chloride is supplied to said gaseous medium f-rom a source external of said sintering zone and also external of the green pressed blanks introduced into saidzoneifor heat treatment therein. 7

No references: cited.

tin: powder is" 

1. THE PROCESS OF MAKING METALLIC PARTS STARTING WITH A METALLIC MATERIAL CONSISTING ESSENTIALLY OF AT LEAST ONE OF THE RELATIVELY DIFFICULTY CHLORIDIZABLE METALLIC POWDERS SELECTED FROM THE GROUP WHICH CONSISTS OF (A) THE METALS; IRON,COPPER, NICKEL AND COBALT AND MIXTURES AND ALLOYS CONSISTING ESSENTIALLY OF AT LEAST TWO OF SAID METALS, (B) MIXTURES AND ALLOYS CORRESPONDING GENERALLY TO BRONZE AND CONSISTING ESSENTIALLY OF UP TO ABOUT 10% TIN AND THE BALANCE COPPER, (C) MIXTURES AND ALLOYS CORRESPONDING GENERALLY IN COMPOSITION TO FERROUS BASE ALLOYS AND CONSISTING ESSENTIALLY OF: UP TO ABOUT 4% CARBON, UP TO ABOUT 20% TUNGSTEN, UP TO ABOUT 1.75% MANGANESE, UP TO ABOUT 28% CHROMIUM, UP TO ABOUT 81/2% MOLYBDENUM, AND THE BALANCE IN ANY SUCH COMPOSITION IRON, WHEREIN IRON IS PRESENT IN A PREDOMINANT AMOUNT; SAID PROCESS COMPRISING THE STEPS OF COMPACTING A PREDETERMINED AMOUNT OF SAID MATERIAL BY MECHANICAL PRESSURE TO FORM IT INTO A GREEN PRESSED BLANK HAVING A SHAPE AND SIZE PREDETERMINED IN ACCORDANCE WITH THE SHAPE AND SIZE OF THE PART TO BE MADE, AND THEREAFTER HEAT TREATING SAID GREEN PRESSED BLANK IN A NON-OXIDIZING ATMOSPHERE CONTAINING AT LEAST ABOUT 0.1% OF GASEOUS HYDROGEN CHLORIDE BY VOLUME, AND WHEREIN SAID HYDROGEN CHLORIDE IS INTRODUCED INTO SAID ATMOSPHERE FROM A SOURCE SEPARATE AND INDEPENDENT OF ANY CHLORIDE WHICH MAY BE PRESENT IN ADMIXTURE IN SAID METALLIC MATERIAL, BY RAISING THE TEMPERATURE OF SAID MATERIAL OF SAID BLANK TO A POINT AT WHICH AT LEAST ONE METAL PRESENT IS BROUGHT TO THE POINT OF INCIPIENT FUSION IN SAID ATMOSPHERE, AND BY SUPPLYING HYDROGEN CHLORIDE GAS TO SAID ATMOSPHERE FROM A SOURCE INDEPENDENT OF THE MATERIAL MAKING UP THE PARTS BEING TREATED. 